of london



' Sept. 21 1926.

B. B. JOHNSON ET AL TELEPHONE SYSTEM Fil'ed Nov. 3, 1922 fm flnibls W rwflm 7%M? "1 f 4 m4 Patented Sept. 21, 1926.

'umree stars were? rrice.

BENJAMIN BERTIE JOHNSON, or LONDON, ENGLAND, AND FERNAND HENRI NI OLAS HAIVIES, or PARIS, FRANCE, AssIe oNs TO THE RELAY AUTOMATIC TELEPHONE COMPANY, LIMITED, or LONDON, ENGL ND.

TELEPHONE SYSTEIVL.

. Application filed November 3, 1922, Serial No. 598,838, and injGreat BritainN Ovember 17, 19 21.

Our invention relates topimprovements in telephone systems and particularly to means for calling the attention of wanted parties.

The usual method of calling a wanted party isby applying a low frequency alternating or pulsating current to the line for the purpose of actuating a bell at the sub- ,scribers station. p

In local battery systems it is well known to apply to a subscribers line a comparatively high frequency alternating or pul sating current for the'purpose of giving an audible signal or howl in his receiver and this principle has been applied in both local and central battery systems to call' thel attention of a subscriber who has left there" ceiver off its hook. V v v It has been suggested to apply this prin-' ciple of applying high or audible frequency currents to subscribers lines in central battery systems as the normal method of calling and so tomodify the circuit sat a subscribers station that the receive-r shallbe.

normally includedin' thelinecircuit, the

line being kept open to direct current by the inclusion in series therewlth of a'condenser.

An exchange working exclusively on this system would have the disadvantage that whilst the, howl produced in the receiver upon the application of the high frequency. current would be .sufiiciently loud for those instruments which were placed in quiet According to our ,,inventi0n,we provide telephone system some of the lines of which are furnished'zwith 'a'call bell while in others the receiving telephone is normally connected directly or inductively to the line and at the exchange serving these lines there are means whereby any subscriber may be called no matter whether his line is of the first or the second class. Preferably one and the same operation at the exchange applies to a wantedline both a howler current and a low frequency ringing current Alternatively lines having'bells may be connected to a difierent numerical group from that to which are connected the lines whose receivers are adapted for calling purposes, a low frequency ringing current being applied to a wanted line connected to the first group,

while a high'frequency current is applied to a wanted line connected to the second] group.

The accompanying drawing illustrates our lllVGIllZlOll inconnexion with a ringing group, which haselsewhere been described as applied. to an automatic telephone system in which the entire switching is done by means of relays. convenienceonly. As the system referred to is well known and as'an understanding of the system'is not necessarv-t'o an understanding of our present invention, it is not described here; Tt will be obvious to any one skilledin the science, however, that-our invention can beequally welliapplied to any ofthe arrangement shown inFigure 3, with an induction coil interposed between the li'neand the receiver.

It will be noticed that in the part Y in Figure 1 there are two'trans'formers HF and LF with primaries P and P and secondaries S and'S"respectively.

HF and vLF indicate that/"the transformers deal, respectively withhigh and'l'ow frequency alternating or pulsating currents, The high and low frequency currents can be obtained in any well known manner such] as from a high speed current interrupter.

CB and an alternator AR.

The secondaries S and S" maybe joined together as shown in. Figure 1, one end of S being connected to a distributor D; Inseries with S and in parallel with S is a condenser C. lVith this arrangement the howler current will be superimposed on the ringing current. a I

The condenser C is of toosmall capacity to short-circuit the low frequency ringing;

On the other hand, it constitutes a by-pass This we have done for arranged that thereceiver isin series with w the line and a condenser when resting upon its support. Figure 3 showsamodification for the high frequency signalling currents which cannot pass through the comparatively high reactance of transformer LF.

Alternatively, the secondaries S and S" may as shown in Figure 1 be connected to the distributor D independently of one another so that the, howler and ringing currents will .be. applied to the wanted line alternately.

The operation of ringing is thefs'ame in each case and is as follows:

lVhen'a connexion shall have been established relay 1TB will be energized in circuit27 whereby circuit-29 will be completed through relafy KG. Relay RG operates and connects ringing lead 31 of the ringinggroup to. the A. wire. If the instrument of the war'ited line be of thetype Figure 3 or- 3 thehi'gh frequency current will by passing through condenserC cause a howl inthe receiver. 1 If, on the other hand, the instrument bejof the type of Figure Qthe lowfrequency current will ring the bell thereof.

The removal of the receiver in either case will by completing the loop permit relay RT'to operate; This will remove a short circuit from across relay RTX' which'will 'operate in the extension 29 of circuit 29 to cut 'out relay RG. This relay will now release owing to the fact that at this time the line wire to which RG is connected is.

' itself connected to earth through the winding of the well known current feeding relay. The operation of relay RTX and release of I relay RG will complete the talking circuit through the ringing group. 7 I H I V If the lines having bells are connected to one numerical group and'the lines whose receivers are normally connected conductively or inductively to the lines are connected to another numerical group different ringing. arrangement will be used when connexion is desired with a line of one group from those which would be used if. a connexion be desired with a line of the other group. These ringing arrangements may be of the type shown in Figure land may be arranged so that those associated with the numerical group to which the bell instruments are allocated have connected to distributor D an alternator and that those associated with the numerical group to which the receiver instruments are allocated have connected to distributor D a high fro and an apparatus adapted for connection-to either line, said apparatus loeingfurther adapted non-selectively to project to either 7 line two signalling currents, the'firs't said telephone line being provided with an 1 1 ratus for efie'ctively responding to one of said signalling currents there being no apparatus for 'eflectively responding to the other said current and the said second telephone line being provided with a d'ifierent apparatus forelfectively responding to the second said current there being no apparatus for responding to thefirst said current.

2. In a telephone system, the combination of a number of lin'es ineach of which a subscribers instrument includes a bell, a

number of lines in' each of which the subscri'bers telephone is normally connected to the line, and means at the exchange'for supplying" to awanted linehigh frequency current .and low frequency current alternately.

3, In a telephone system, automatic means for supplying to a wanted line both a howler current and 'alow frequency ringing current and means operable upon the response of {the called subscriber for disconnecting such currents from the line.

In testimony that we claim the foregoing V v as our invention we have signed our names this. 13th day 4 of October 1922.

BENJAMIN BERTIE 'JOHllSON. I FERNAND HENRI NICOLAS uAMr'sy 

